The present invention generally relates to systems for loading and/or unloading fluids for ships, commonly referred to as marine loading systems. These systems are used to transfer a liquid or gaseous product between a ship and a quay or between two ships.
More particularly, the present invention relates to the devices for controlling movement and positioning of such loading and/or unloading systems.
Generally, marine loading systems have a fluid transfer line end that is fixed to a base and connected to a tank of fluid to be transferred, and an opposite line end that is moveable and provided with a coupling adapted for connecting to a target duct, itself connected to a fluid tank.
Two families of fluid loading systems for ships are known, which are distinguished by their structure: systems for transfer by rigid pipes and systems for transfer by flexible pipes.
In the family of systems for transfer by rigid pipes, loading arm systems and pantograph systems can be distinguished.
The loading arm is an articulated tubing arrangement, having a base, connected to fluid tank, on which there is mounted a first pipe, designated inner pipe, via a portion of tube with a 90° bend enabling rotation of one of its ends about a vertical axis, and the other end about a horizontal axis. At the opposite end of the inner pipe, a second pipe, designated outer pipe, is rotatably mounted about a horizontal axis. A coupling is mounted at the end of the outer pipe.
Each of the three rotations is controlled by a jack or hydraulic motor with an on/off control. The operator has a command interface enabling him to control each of the movements independently.
The pantograph systems, like the loading arms, have a base connected to a tank. A crane is rotatably mounted on that base. The crane has a boom carrying a pipe for the fluid. At the end of the boom there is mounted a pantograph composed of articulated pipes for the fluid, and enabling a coupling to be moved that is mounted at the free end of the pantograph. The inclination of the pantograph is controlled by a rotation at the end of the boom. The movement of the pantograph is controlled by hydraulic motors and by a jack for the rotation on the base.
Lastly, the flexible piping systems generally have a line in which is conveyed the fluid product and a mechanical system enabling the line to be maneuvered. There are several types of maneuvering systems, but in all cases they include a manipulating crane or structure which supports the coupling for connecting the flexible piping.
In practice, in most of the systems, the coupling is freely articulated at its end with regard to three rotations, so as to be able to be manipulated manually and precisely by an operator when the coupling is presented to the target duct, for the connection.
These two families of loading devices have structural differences, but their control systems are designed according to the same general principle of operation. It is noted that, in all cases, the coupling has at least three degrees of freedom relative to the base bearing the fixed end of the duct, and that the movements in each of these degrees of freedom are independently controlled by actuators.
Each actuator is separately controlled by an independent control of on/off type. The operator can act independently on each of the controls to control a particular member of the loading system. The combined action on the group of actuators enables the coupling to be positioned at a desired point in space.
In general, the actuators used are hydraulic, for example a hydraulic motor or jack, but the use of electric actuators is also known, for example electric motors, or pneumatic actuators. In all cases, the actuators equipping marine loading systems are controlled by on/off control, with a constant speed of movement, and in certain cases, with the possibility of setting two speeds of movement at will.
In practice, these control devices are delicate to implement, in that the operator must know the kinematics of the marine loading system perfectly and simultaneously combine the movement of each of the actuators independently so as to obtain, by summing all the movements, a combined movement of the coupling corresponding to the movement he desires to give to it. As the movements are generated by actuators with on/off control at a fixed speed, it is difficult or even impossible for the operator to generate movement of the coupling that is rectilinear and/or at constant speed. More generally, it is difficult for the operator to precisely master the movement of the coupling, which increases the risks of the coupling striking against obstacles or against the target duct. This may damage the seals of the coupling.